Neisseria gonorrhoeae, a pathogenic agent of gonorrhoeae, is the major cause of sexually transmitted diseases (STD) in the United States, and there is currently no effective vaccine. Previous investigations using several cell surface components have failed in the developing of gonococcal vaccine due to the common drawback of antigenic variability and phase variation. Recently, an important virulence gene encoding the outer membrane adhesin/invasin protein has been discovered in the genome of pathogenic N. gonorrhoeae, which provide potential possibility to develop an effective vaccine against gonococcal diseases. This project is to study the vaccine potential of this selected protein from N. gonorrhoeae. This project will (1) evaluate the sequence variation of this gene of diverse N. gonorrhoeae strains from different sources, (2) investigate the immunogenicity of its recombinant protein and biological function of this gene, and (3) demonstrate if antibodies raised from this protein confer to protective immunity against gonococcal diseases. Several techniques will be used in this project including PCR, nucleotide sequencing, gene cloning and expression, gene knocking out, animal immunization, bactericidal and adhesion assays. The data from this project will provide fundamental information for understanding the role of this protein in N. gonorrhoeae and the possibility to develop a gonococcal vaccine.